1. Technical Field
The present invention is generally directed to a LCD (liquid crystal display) panel and device for use in a portable personal computer (PC). In particular, the present invention is directed to a LCD panel and LCD device that provides improved brightness and viewing angle of light emitted from a portable LCD panel.
2. Description of Related Art
There has been remarkable progress in the use of liquid crystal display devices as image displays for PCs and various other applications. The liquid crystal display devices of this kind are typically constructed such that a backlight unit, which comprises a planer light source for illumination from the backside of the liquid crystal display panel, illuminates an entire liquid crystal layer having a given expanse with light having a uniform brightness thereon, wherein an image formed in the liquid crystal layer is made visible using polarizing sheets.
This backlight design typically employs a HCFL (hot-cathode fluorescent lamp) or a CCFL (cold-cathode fluorescent lamp) as the light source. Light from so-called xe2x80x9clinear light sourcexe2x80x9d such as a fluorescent tube must be projected onto the full surface of the liquid crystal display panel, and two general configurations for the backlight have been developed: (i) a directly-below type; and (ii) a side light type (edge lit type). A directly-below backlight unit employs one or more fluorescent tubes disposed directly below the LCD panel, with a light control plate and a diffusing plate disposed between the fluorescent tube(s) and the LCD panel.
A side light type unit has a fluorescent tube along one or two sides of a light guide plate that is made of a transparent resin. The light guide plate directs light incident on the edges of the light guide plate toward the surface of the liquid crystal display panel by reflecting microstructured portions formed on the backside of the light guide plate. This backlight design is suitable for use as a display device for portable equipment such as a notebook PC or the like, since it can be made thin as compared to a backlight device comprising a directly-below structure.
A desired characteristic for a liquid crystal display device is that the display be bright even from a wide viewing angle. One method of increasing the brightness of the screen is to increase the luminance of the backlight. Increasing the backlight luminance, however, has the disadvantage of increased power consumption, especially in the case of battery powered portable equipment, wherein power consumption should be limited.
Typically, to increase the viewing angle of a display, a diffusing plate is used in the liquid crystal device. The diffusing plate redistributes light from the light guide plate as light having a wider angular distribution. A diffusing plate comprises a light diffusing layer, made of a light transmissive resin and light scattering particles such as acrylic particles, silica particles or the like, on or in the surface of a transparent substrate such as a PET film. When light emitted from a light source (such as a fluorescent tube or the like) is transmitted through the diffusing plate, however, the luminance is substantially reduced. Consequently, by removing the diffusing plate, the luminance, or brightness, of the liquid crystal display device can be increased.
As noted above, however, the diffusing plate provides an important function of increasing the angular distribution of the light from the backlight to provide a wider viewing angle. Thus, it is not desirable to remove the diffusing plate.
There are patents that disclose the use of lenticular lens sheets in conjunction with liquid crystal displays. This use of microlens has generally been directed toward projection displays (see, U.S. Pat. Nos. 5,764,319, 5,548,349, and 5,859,675), especially for xe2x80x9ccolor-filterlessxe2x80x9d projection displays where a lenticular sheet with a lens pitch equal to the pixel pitch is used to focus and direct Red, Green, and Blue light which are incident on the lenticular sheet from different angles through spatially separate Red, Green, and Blue subpixels in the display.
A color filterless backlight system for direct view LCDs is described in U.S. Pat. No. 4,798,448 and U.S. patent application Ser. No. 09/664,719 filed Sep. 19, 2000, entitled xe2x80x9cFLAT BACKLIGHTING SYSTEMxe2x80x9d, which is commonly assigned and incorporated herein by reference. U.S. Pat. No. 5,101,279 to Kurematsu et al. describes using a lenticular sheet in combination with a LCD to increase the amount of light transmitted through the open aperture. In this patent, the longitudinal axes of the cylindrical lenses comprising the lenticular extends in the direction of the optical switching portion (open aperture) dimension of greater distance. This configuration has a number of disadvantages. Nearly all LCDs use a vertical triad structure, i.e., each pixel is composed of a Red, Green, and Blue subpixel, each of which extends vertically across the whole of a square pixel and occupies ⅓ of the pixel area in the horizontal direction. For the configuration described by Kumematsu et al., the lenticular longitudinal axis would be vertical and the pitch would equal ⅓ of the pixel pitch. It would be advantageous to make the pitch of the lenticular equal to the pixel pitch (and not the subpixel pitch) since less precision is needed in forming and aligning the lenticular sheet to the display. If a vertical lenticular is placed behind the display, and no additional structure is added to the front, the width of the output light distribution would be increased in the horizontal direction, but be unchanged in the vertical direction.
It is typical for notebook displays to use a tapered light guide with the CCFL along the top or bottom edge of the display. This is advantageous since nearly all displays are used in a xe2x80x9clandscapexe2x80x9d mode so the top or bottom edge is longer than the side edges. Thus, placing a single CCFL along the longer edge results in a brighter display than placing a single CCFL along the shorter edge. As described below, with a tapered light guide having the CCFL along the bottom (or top) edge, the light output distribution in the vertical direction can be adjusted to be much less than that in the horizontal direction, so having a vertical lenticular present which further increases the width of the output light distribution in the horizontal direction is very undesirable.
It is an object of the present invention is to provide a liquid crystal display panel and a liquid crystal display device capable of improving the brightness and viewing angle of the light emitted from a portable liquid crystal display panel.
In one aspect of the present invention, a display panel for a direct view display device comprises: a first substrate comprising a light transmissive material for receiving light emitted from the light source; a second substrate comprising a light transmissive material for receiving light transmitted through the first substrate and emitting the light from an image display screen thereof; an optical device layer, disposed between the first and second substrates, comprising an optical device for controlling light emitted from the light source; and light converging means for converging the light emitted from the light source on the optical device layer.
The light converging means preferably converges light emitted from the light source onto the optical device layer so that the converged light can be transmitted through the optical device layer without being blocked, e.g., by scanning lines. Further, the focusing of light in one dimension increases the angular width of the output distribution in that direction, which increases the viewing angle without using diffusing plates. In other words, since light having a wide angular distribution can be emitted from the display panel without using any diffusing plates, unlike the conventional method, it is possible to increase the luminance while maintaining adequate brightness off the display normal to provide a wide viewing angle. In addition, by properly setting the converging position (or focal point) of the converging means, it is possible to partially prevent the reduction in transmission of light due to light blocking portions of a TFT panel.
In another aspect of the present invention, the display panel comprises a plurality of pixels arrayed in a dot matrix form and the light converging means is preferably formed to correspond to columns of the pixels or, alternatively, to rows of the pixels. In a preferred embodiment, the light converging means comprises a plurality of lenticular lenses, wherein one lenticular lens is provided for each column or row of pixels. In another embodiment, the light converging means comprises a fly-eye lens.
In another aspect of the present invention, a LCD (liquid crystal display) panel comprises: an array substrate comprising rectangular pixels in a matrix form, each of the pixels comprising a pair of long sides and a pair of short sides; a color filter substrate; a liquid crystal layer disposed between the array substrate and the color filter substrate; and a plurality of lenticular lenses extending along the short sides of the pixels for converging light to desired locations within the LCD panel, wherein the lenticular lenses are disposed on a surface side of the array substrate that receives light from a light source and wherein the lenticular lenses are disposed such that a boundary between adjacent lenticular lenses is substantially arranged along the short sides of pixels.
Preferably, with the LCD panel, the light is first converged by the lenticular lens to a location between the array substrate and the color filter substrate, then transmitted through the color filter substrate while being diffused with a predetermined angle, transmitted through a polarizing plate of the LCD panel, and then emitted with an angle that is greater than the predetermined angle.
In a liquid crystal display panel of the invention, preferably, each of the lenticular lenses focuses the light in the liquid crystal layer and each of the lenticular lenses preferably focuses light within a range of projection surfaces of the pixels such that light is prevented from being blocked by scanning lines formed on the array substrate. In other words, irrespective of an open area ratio, the luminance of the liquid crystal display panel can be enhanced.
A liquid crystal display panel according to the present invention may be implemented in a direct-view liquid crystal display device to increase luminance and viewing angle. In such a case, a gap between a pair of short sides of a pixel is set in a range of about 100 micrometers to about 300 micrometers.
In another aspect of the present invention, a liquid crystal display device comprises: a liquid crystal display panel comprising a liquid crystal layer and an image display screen; a light source for emitting a light to the liquid crystal display panel; and a lens disposed between the liquid crystal display panel and the light source for converging the light emitted from the light source inside the liquid crystal display panel, wherein the light emitted from the light source is converged inside the liquid crystal display panel, then diffused with a first angle, and emitted from the image display screen with a second angle that is greater than the first angle.
A liquid crystal display panel and device according to the present invention can advantageously emit light having a wide radiation distribution, without having to employ diffusing plates to obtain such wide radiation distribution. The lens converges light emitted from the light source on the liquid crystal layer or, alternatively in the vicinity thereof, and then the converged light is diffused with a first angle, and then emitted from the image display screen with a second angle that is larger than the first angle.
Preferably, in a liquid crystal display device of the invention, a half-value width (an angle at which luminance is half of the maximum luminance) of the light emitted from the image display screen is set larger than a half-value width of the light emitted from the light source in one direction. Specifically, the angle is preferably increased in the direction perpendicular to the lenticular lens axis.
In addition, in a liquid crystal display device of the invention, a half-value width of the light emitted from the light source is preferably set in a range from about xe2x88x9215 degrees to about xe2x88x925 degrees on one side of the normal direction and in the range of about 5 degrees to about 15 degrees on the opposite side of the normal.
Further, in a liquid crystal display device of the invention, a half-value width of the light emitted form the image display screen is preferably set in a range of about xe2x88x9230 degrees to about xe2x88x9215 degrees on one side of the display normal and in the range of about 15 degrees to about 30 degrees on the opposite side of the normal.
In another aspect of the invention, the liquid crystal display device further comprises: a light guide plate for guiding the light emitted from the light source to the liquid crystal display panel, the light guide plate comprising a light bending structure formed in a light emission surface thereof; a light bending sheet, disposed between the light guide plate and the liquid crystal display panel, comprising a light bending structure formed in a surface facing the light emission surface of the light guide plate that intersects with the light bending structure formed in the light guide plate; and a lenticular lens disposed in a surface of the liquid crystal display panel facing the light bending sheet.
In this embodiment, preferably, the liquid crystal display panel does not have a lens structure on the image display screen side. Further, the light bending structure (e.g., a prism structure) of the light guide plate is preferably formed in a light advancing direction in the light guide plate.
In another aspect of the invention, a liquid crystal display device comprises: a liquid crystal display panel comprising an array substrate comprising a plurality of signal lines for supplying display signals and a plurality of scanning lines for supplying scanning signals, wherein the signal and scanning lines are arrayed in a matrix form, a color filter substrate disposed oppositely to the array substrate with a predetermined gap therebetween, and a liquid crystal layer disposed in the gap; a light guide plate, disposed in a backside portion of the liquid crystal display panel, comprising at least one light incident surface and a light emission surface for emitting a light made incident from the light incident surface; a lamp disposed along the light incident surface of the light guide plate; and a plurality of lenticular lenses disposed between the light guide plate and the liquid crystal display panel and extending in a direction parallel to the scanning lines.
In a liquid crystal display device of the invention, light emitted from the lamp is projected through the light guide plate onto the lenticular lens. The light projected on the lenticular lens is converged within the range of the array substrate to the color filter substrate. The converged light is diffused with a predetermined angle, and emitted to the outside of the liquid crystal display panel after the passing through the color filter substrate. In this case, the emitting light is radiated with a wider angle because of a difference in refractive indices between the liquid crystal display panel and air.
Further, in a liquid crystal display device of the invention, the array pitch of the plurality of lenticular lenses preferably coincides with the pitch of the scanning lines. In addition, the light emission surface of the light guide plate preferably comprises a plurality of prisms that extend in a direction parallel to a light advancing direction in the light guide plate, and the light bending sheet is preferably disposed between the light guide plate and the lenticular lenses, wherein the light bending sheet comprises a plurality of prisms that extend in a direction perpendicular to the light advancing direction in the light guide plate. In this way, the degree of convergence of light projected to the lenticular lens can be increased.
These and other aspects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments, which is to be read in connection with the accompanying drawings.